Outside groups have spent more than $1 billion trying to influence this year's election, and the tidal wave of special interest money so no signs of abating in the 10 days that remain before Election Day.

The total, tabulated by Sunlight's Follow the Unlimited Money, is especially mind-boggling considering that it comes in a campaign that has focused largely on the anemic economy and underscores the changed landscape in the first presidential campaign to be contested following the Supreme Court 2010 decision in Citizens United, which opened the door for deep-pocketed donors to flaunt their wealth in ways unimaginable before, with a seemingly non-stop stream of six- and seven-figure checks.

Outside groups' $1 billion has funded an overwhelmingly negative shadow campaign: More than 80 percent of the spending has gone to oppose, rather than support, candidates. And it includes $219 million in dark money -- donations from nonprofit organizations which, because of their tax-exempt status, will never have to disclose their donors.

Outside spending has been accelerating at an exponential rate in the closing weeks of the campaign, from $14.5 million in the week ending Sept. 1 to more than $110 million last week. On Thursday alone, Follow the Unlimited Money clocked more than $9 million in outside expenditures, the largest to fund ads against President Barack Obama, but also including donations for and against many House and Senate candidates.

Recently, the outside spending totals also have included an uptick in expenditures for electioneering -- communications that often strongly tout or denigrate a candidate but stop short of directly advocating for his or her election or defeat. Electioneering spending dropped after a court ruled that nonprofit groups engaged in it would have to report donors, but appear to be coming back strong after an appellate court overturned that decision.